Electrical stimulation of body tissues and nerves is widely used for various indications. Several approaches are known which deliver electrical stimulation to the targeted body area or organ. Some approaches require focused delivery of the stimulation, while others require less targeted stimulation.
Transcutaneous electrical nerve stimulation (commonly referred to as TENS) involves providing electrical signals through the skin for stimulating nerves by attaching electrodes to the skin surface. TENS is advantageous in being non-invasive. However, its effectiveness is questionable since the delivered stimulation is not focused and only a small fraction of the electrical signals delivered through the skin is used effectively. The electrodes attached to the skin surface cannot select specific body areas, for example particular muscles or deeper muscle tissue. TENS is generally limited to pain relief. However, since the stimulation can be sensed by receptors in the skin, TENS can cause discomfort due to stimulation-induced pain.
Alternatively, percutaneous stimulation can be used to deliver targeted, effective stimulation without activating the skin receptors. A lead is implanted in bodily tissues and led through the skin for connection to an external stimulator. Electrical signals are delivered through the lead to the bodily tissues. However, percutaneous stimulation is not widely practiced since percutaneous leads are unaesthetic and unhygienic, providing a conduit for infection.
Miniature implantable stimulators, for example, the RF BION® device (Advanced Bionics Corporation, California, USA) deliver focused stimulation, while not violating skin integrity. The implanted stimulator can be connected to an implanted lead to position the stimulator close to the skin, while delivering stimulation to deeper body areas. The miniature implanted stimulator requires the delivery of energy from outside the body, which is usually accomplished by an external coil in proximity to the skin to generate a low-frequency magnetic field. A disadvantage of the RF BION® device is the necessity for an external coil. The battery-powered BION® stimulator (Advanced Bionics Corporation) avoids this problem. The BION® stimulator is a miniature implantable stimulator containing a miniature rechargeable battery. The battery can be charged wirelessly using a charging coil, with a relatively short charging time. However, such implantable stimulators are not generally desirable due to their expense.
A system which overcomes the above problems of the current techniques is the “router system” as described in International Publication No. WO 2005/070494 A1 to Prochazka, published Aug. 4, 2005 and claiming priority from U.S. Provisional Patent Application No. 60/538,618 filed Jan. 22, 2004 (Neural Prosthesis Program Meeting, NIH Meeting, November 2004; Gan et al., 2005). The router system is based on a passive electrical conductor (for example, a lead) which extends from subcutaneous tissue located below a surface cathodic electrode to the target body tissue. The electrical conductor has a pick-up end for allowing the electrical current to flow through the conductor, and a stimulating end for delivering electrical current to the target body tissue. A surface anodic electrode is also positioned on the skin. Advantageously, the router system applies sub-sensational levels of transcutaneous stimulation, thereby avoiding stimulation-induced pain. Importantly, focused delivery of the stimulation to the target body tissue is achieved via the passive electrical conductor. Due to such significant advantages, further developments of the router system are desirable.